[PATCH v9 16/22] KVM: arm64: Apply dynamic guest counter reservations

[Colton Lewis]

Reserve and release guest PMU counters dynamically during vCPU load and
put rather than statically at VM creation.

Add kvm_pmu_set_guest_counters() in arch/arm64/kvm/pmu-direct.c, called
from kvm_pmu_load() and kvm_pmu_put(). When the requested guest counter
mask collides with active host events in cpuc->used_mask (or when
releasing counters after squeezing a host event), invoke
perf_pmu_resched_update() with kvm_pmu_update_mask() to update the
per-CPU cpuc->cntr_mask between scheduling host events out and back in;
otherwise update cpuc->cntr_mask directly with interrupts disabled.

Signed-off-by: Colton Lewis <coltonlewis at google.com>
---
 arch/arm64/kvm/pmu-direct.c  | 77 ++++++++++++++++++++++++++++++++++++
 include/linux/perf/arm_pmu.h |  1 +
 2 files changed, 78 insertions(+)

diff --git a/arch/arm64/kvm/pmu-direct.c b/arch/arm64/kvm/pmu-direct.c
index a22c9258c2452..31d5afc44f36e 100644
--- a/arch/arm64/kvm/pmu-direct.c
+++ b/arch/arm64/kvm/pmu-direct.c
@@ -115,6 +115,77 @@ u64 kvm_pmu_direct_pmcr_read(struct kvm_vcpu *vcpu)
 		ARMV8_PMU_PMCR_N);
 }
 
+/* Callback to update counter mask between perf scheduling */
+static void kvm_pmu_update_mask(struct pmu *pmu, void *data)
+{
+	struct arm_pmu *arm_pmu = to_arm_pmu(pmu);
+	struct pmu_hw_events *cpuc = this_cpu_ptr(arm_pmu->hw_events);
+	unsigned long *new_mask = data;
+
+	bitmap_copy(cpuc->cntr_mask, new_mask, ARMPMU_MAX_HWEVENTS);
+}
+
+/**
+ * kvm_pmu_set_guest_counters() - Handle dynamic counter reservations
+ * @cpu_pmu: struct arm_pmu to potentially modify
+ * @guest_mask: new guest mask for the pmu
+ *
+ * Check if guest counters will interfere with current host events and
+ * call into perf_pmu_resched_update if a reschedule is required.
+ */
+static void kvm_pmu_set_guest_counters(struct arm_pmu *cpu_pmu, u64 guest_mask)
+{
+	struct pmu_hw_events *cpuc = this_cpu_ptr(cpu_pmu->hw_events);
+	DECLARE_BITMAP(guest_bitmap, ARMPMU_MAX_HWEVENTS);
+	DECLARE_BITMAP(new_mask, ARMPMU_MAX_HWEVENTS);
+	unsigned long flags;
+	bool need_resched = false;
+
+	bitmap_from_arr64(guest_bitmap, &guest_mask, ARMPMU_MAX_HWEVENTS);
+	bitmap_copy(new_mask, cpu_pmu->cntr_mask, ARMPMU_MAX_HWEVENTS);
+
+	local_irq_save(flags);
+	if (guest_mask) {
+		/* Subtract guest counters from available host mask */
+		bitmap_andnot(new_mask, new_mask, guest_bitmap, ARMPMU_MAX_HWEVENTS);
+
+		/* Did we collide with an active host event? */
+		if (bitmap_intersects(cpuc->used_mask, guest_bitmap, ARMPMU_MAX_HWEVENTS)) {
+			int idx;
+
+			need_resched = true;
+			cpuc->host_squeezed = true;
+
+			/* Look for pinned events that are about to be preempted */
+			for_each_set_bit(idx, guest_bitmap, ARMPMU_MAX_HWEVENTS) {
+				if (test_bit(idx, cpuc->used_mask) && cpuc->events[idx] &&
+				    cpuc->events[idx]->attr.pinned) {
+					pr_warn_once("perf: Pinned host event squeezed out by KVM guest PMU partition\n");
+					break;
+				}
+			}
+		}
+	} else {
+		/*
+		 * Restoring to full mask.
+		 * Only resched if we previously squeezed an event.
+		 */
+		if (cpuc->host_squeezed) {
+			need_resched = true;
+			cpuc->host_squeezed = false;
+		}
+	}
+	if (!need_resched)
+		/* Host was never using guest counters anyway */
+		bitmap_copy(cpuc->cntr_mask, new_mask, ARMPMU_MAX_HWEVENTS);
+	local_irq_restore(flags);
+
+	if (need_resched) {
+		/* Collision: run full perf reschedule */
+		perf_pmu_resched_update(&cpu_pmu->pmu, kvm_pmu_update_mask, new_mask);
+	}
+}
+
 /**
  * kvm_pmu_host_counter_mask() - Compute bitmask of host-reserved counters
  *
@@ -255,6 +326,7 @@ static void kvm_pmu_apply_event_filter(struct kvm_vcpu *vcpu)
  */
 void kvm_pmu_load(struct kvm_vcpu *vcpu)
 {
+	struct arm_pmu *pmu;
 	unsigned long guest_counters;
 	u64 mask;
 	u8 i;
@@ -269,7 +341,9 @@ void kvm_pmu_load(struct kvm_vcpu *vcpu)
 
 	preempt_disable();
 
+	pmu = vcpu->kvm->arch.arm_pmu;
 	guest_counters = kvm_vcpu_pmu_guest_counter_mask(vcpu);
+	kvm_pmu_set_guest_counters(pmu, guest_counters);
 	kvm_pmu_apply_event_filter(vcpu);
 
 	for_each_set_bit(i, &guest_counters, ARMPMU_MAX_HWEVENTS) {
@@ -329,6 +403,7 @@ void kvm_pmu_load(struct kvm_vcpu *vcpu)
  */
 void kvm_pmu_put(struct kvm_vcpu *vcpu)
 {
+	struct arm_pmu *pmu;
 	unsigned long guest_counters;
 	unsigned long flags;
 	u64 mask;
@@ -345,6 +420,7 @@ void kvm_pmu_put(struct kvm_vcpu *vcpu)
 
 	preempt_disable();
 
+	pmu = vcpu->kvm->arch.arm_pmu;
 	guest_counters = kvm_vcpu_pmu_guest_counter_mask(vcpu);
 	mask = guest_counters;
 
@@ -395,5 +471,6 @@ void kvm_pmu_put(struct kvm_vcpu *vcpu)
 	write_sysreg(val & mask, pmovsclr_el0);
 	local_irq_restore(flags);
 
+	kvm_pmu_set_guest_counters(pmu, 0);
 	preempt_enable();
 }
diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
index be1e345e99a77..45658273ffa86 100644
--- a/include/linux/perf/arm_pmu.h
+++ b/include/linux/perf/arm_pmu.h
@@ -76,6 +76,7 @@ struct pmu_hw_events {
 
 	/* Active events requesting branch records */
 	unsigned int		branch_users;
+	bool host_squeezed;
 };
 
 enum armpmu_attr_groups {
-- 
2.56.0.rc1.310.g51773c2048-goog